The present invention relates generally to binary switches for use in the medical monitoring field and to methods for manufacturing same. More particularly, the instant invention involves the construction, manufacture, and operation of pressure sensitive patient monitors of the sort commonly used in medical settings to detect when a patient has, for example, left a chair or a bed.
It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. These individuals are often afflicted by gait and balance disorders, weakness, dizziness, confusion, visual impairment, and postural hypotension (i.e., a sudden drop in blood pressure that causes dizziness and fainting), all of which are recognized as potential contributors to a fall. Additionally, cognitive and functional impairment, and sedating and psychoactive medications are also well recognized risk factors.
A fall places the patient at risk of various injuries including sprains, fractures, and broken bonesxe2x80x94injuries which in some cases can be severe enough to eventually lead to a fatality. Of course, those most susceptible to falls are often those in the poorest general health and least likely to recover quickly from their injuries. In addition to the obvious physiological consequences of fall-related injuries, there are also a variety of adverse economic and legal consequences that include the actual cost of treating the victim and, in some cases, caretaker liability issues.
In the past, it has been commonplace to treat patients that are prone to falling by limiting their mobility through the use of restraints, the underlying theory being that if the patient is not free to move about, he or she will not be as likely to fall. However, research has shown that restraint-based patient treatment strategies are often more harmful than beneficial and should generally be avoidedxe2x80x94the emphasis today being on the promotion of mobility rather than immobility. Among the more successful mobility-based strategies for fall prevention include interventions to improve patient strength and functional status, reduction of environmental hazards, and staff identification and monitoring of high-risk hospital patients and nursing home residents.
Of course, direct monitoring of high-risk patients, as effective as that care strategy might appear to be in theory, suffers from the obvious practical disadvantage of requiring additional staff if the monitoring is to be in the form of direct observation. Thus, the trend in patient monitoring has been toward the use of electrical devices to signal changes in a patient""s circumstance to a care giver who might be located either nearby or remotely at a central monitoring facility, such as a nurse""s station. The obvious advantage of an electronic monitoring arrangement is that it frees the care giver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single person can monitor multiple patients which can result in decreased staffing requirements.
Generally speaking, electronic monitors work by first sensing an initial status of a patient, and then generating a signal when that status changes, e.g., he or she has sat up in bed, left the bed, risen from a chair, etc., any of which situations could pose a potential cause for concern in the case of an at-risk patient. Electronic bed and chair monitors typically use a pressure sensitive switch in combination with a separate electronic monitor which conventionally contains a microprocessor of some sort. In a common arrangement, a patient""s weight resting on a pressure sensitive mat (i.e., a xe2x80x9csensingxe2x80x9d mat) completes an electrical circuit, thereby signaling the presence of the patient to the microprocessor. When the weight is removed from the pressure sensitive switch, the electrical circuit is interrupted, which fact is similarly sensed by the microprocessor. The software logic that drives the monitor is typically programmed to respond to the now-opened circuit by triggering some sort of alarmxe2x80x94either electronically (e.g., to the nursing station via a conventional nurse call system) or audibly (via a built-in siren) or both. Additionally, many variations of this arrangement are possible and electronic monitoring devices that track changes in other patient variables (e.g., wetness/enuresis, patient activity, etc.) are available for some applications.
General information relating to mats for use in patient monitoring may be found in U.S. Pat. Nos. 4,179,692, 4,295,133, 4,700,180, 5,600,108, 5,633,627, 5,640,145, and 5,654,694 (concerning electronic monitors generally). Additional information may be found in U.S. Pat. Nos. 4,484,043, 4,565,910, 5,554,835, and 5,623,760 (switch patents), the disclosures of all of which are all incorporated herein by reference.
By way of general background, in a typical arrangement, a pressure-sensing mat of the sort discussed herein is a sealed xe2x80x9csandwichxe2x80x9d composed of three layers: two outer layers and an inner (central) layer positioned between the two outer layers. The outer layers are usually made of some sort of plastic and are impermeable to fluids and electrically non-conductive on their outer faces, where xe2x80x9couterxe2x80x9d is determined with respect to the middle layer. The inner surface of each of the outer layersxe2x80x94which inner surfaces are oriented to face each other from opposite sides of the central layerxe2x80x94is made to be electrically conductive, usually by printing a conductive (e.g., carbon-based) ink on that surface. The compressible middle xe2x80x9ccentral spacerxe2x80x9d is made of a non-conductive material and serves to help keep the two conductive faces apart when a patient is not present on the sensor. The central spacer is discontinuous, which makes it possible for the two conductive inner surfaces to be forced into contact through the one or more discontinuities when weight is applied to the switch. By attaching a separate electrical lead to each of the conductive inner faces, it can readily be determined via a simple continuity (or low voltage) check whether a weight is present on the sensor (e.g., a patient is seated thereon). Removal of the weight causes the central spacer to expand and press apart the two conducting faces, thereby breaking the electrical connection between them. Thus, a device that monitors the resistance across the two electrical leads may determine when a patient has moved from a seated or prone position.
One disadvantage of the current generation of pressure sensitive mats is that they cannot be completely (e.g., hermetically) sealed around their perimeters against the external environment. The reason for this should be clear: if the interior of the mat were completely sealed, air pressure inside of the mat would tend to oppose the urging of the mat faces into contact, thereby making it difficult or impossible to complete the circuit (e.g., think of compressing an xe2x80x9cair pillowxe2x80x9d). Of course, the fact that the interior of the mat must be kept open to the atmosphere results in a mat that is highly susceptible to invasion by bodily fluids or cleaning solutions, as the in-rushing air that enters when the switch expands tends to carry fluids along with it into the interior of the mat. Further, it is well known that some common disinfecting cleaners can loosen the adhesives that hold the layers of a conventional mat together, thereby ruining the sensor. Thus, cleaning soiled mats becomes problematic. In summary, what is needed is a pressure sensitive mat that is more resistant to invasion by fluids than has heretofore been available.
Methods of manufacturing conventional pressure sensitive mats for use in medical applications of this sort of sensing device typically begin at a single station punch, wherein the upper and lower plastic/nonconductive members are cut from a larger sheet of material. This step would typically be followed by the application of a conductive material to one face of each member. For example, the conductive material could be printed onto the surface using a carbon-based ink, although other variations have been employed. A popular alternative method involves the use sheets or rolls of material on which the conductor has been pre-applied.
The inner non-conductive member may be a discrete layer of material that has dimensions somewhat smaller than those of the exterior member, or it could take the form of a pattern of non-conductive raised ridges or dots which is deposited on top of the ink (the raised ridges separating the two conductive faces wherever they are present). Either way, the non-conductive material must be discontinuous to the extent that it allows the conductive materials to come into contact when the assembled mat is compressed. Thereafter, separate isolated electrical leads are attached to the inner faces of the mats so that they make contact with the conductive surface. The two conductive inner surfaces are oriented so that they face each other across the insulating layer and, if a separate central spacer is used, it is positioned between them. Finally, the apparatus is sealed at its edges to protect against invasion of moisture, typically through the use of an adhesive that is applied to the edges of the facing members.
However, mats assembled in this manner are subject to a variety of well-known problems. For example, if the non-conductive member is bent, it is possible to introduce breaks in the conductive ink pattern that has been printed thereon. If the break extends the width of the conductive surface, dead (i.e., nonresponsive) regions may be created in the mat or the mat may cease to function altogether.
Additionally, the seal between the two outer members is dependent on the quality of the adhesive bond between them. Depending on the choice of adhesive and the environmental conditions at the time the seal was formedxe2x80x94e.g., the relative humidity, temperature, etc.xe2x80x94the adhesion between the two outer members may be imperfect, which can allow moisture into the interior of the assembled device, thereby shortening its active and or shelf life.
Further, prior art mats are susceptible to cord pull out and may fail to open after being compressed, which failure is often because the air inside has been expelled and air pressure continues to hold the halves of the mat together after weight is removed.
Finally, because of variability that is inherent in the current technology of printing conductive inksxe2x80x94which is typically done via some sort of screening processxe2x80x94the mats produced thereby can be unreliable and it can be difficult to create printed mats that exhibit specific electrical properties when the circuit is closed. Further, the screen process does not lend itself to repeatability, so it can be difficult, say, to produce a mat that has a particular resistance when closed.
Heretofore, as is well known in the patient monitor arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a electronic patient monitor that would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.
In accordance with a preferred embodiment of the instant invention, an apparatus for patient monitoring is taught herein that is constructed via heat sealing according to the methods described hereinafter. The instant method and apparatus are designed to produce a patient monitoring switch that is more reliable and can be manufactured with less cost than has heretofore been available in the prior art.
More particularly and according to a first preferred aspect of the instant invention, there is provided a hermetically sealed binary switch that is constructed of a xe2x80x9csandwichxe2x80x9d of alternating polyester and polyethylene layers. In the preferred embodiment, the mat consists of an upper member, a central spacer, and a lower member. The upper and lower member are both non-conductive on their outer surfaces and conductive on their inner surfaces, which inner surfaces face each other across the central spacer. The upper and lower member are both preferably composed of two elements: an outer nonconductive layer (preferably of a material such as polyester) and an inner nonconductive layer upon which has been deposited a conductor such as aluminum. The central spacer is also nonconductive and is preferably formed of a central core of polyester that has been placed between two layers of polyethylene. Additionally, the central spacer has at least one aperture passing therethrough, the purpose of the aperture being to allow the two conductive elements of the upper and lower members to come into contact when a weight is placed on the mat.
A critical aspect of this embodiment of the instant mat is that its perimeter is hermetically sealed against the atmosphere, thereby making it resistant to fluid invasion during use. Preferably, its interior will have been caused to contain rarified air during manufacture, which makes it possible to compress its two halves together in spite of the sealed perimeter. Alternatively, and in another preferred embodiment, the instant mat will be completely sealed along its perimeter, but a breathing tube will penetrate into the interior of the mat, thereby assisting the movement of air into and out of the mat during use.
According to another preferred mat embodiment, the upper and lower units are each composed of three elements: an outer nonconductive layer (preferably polyester), bonded to an inner adhesive layer (preferably polyethylene), and an inner conductive layer (preferably a layer of polyester upon which has been deposited a conductor such as aluminum). Preferably, the central spacer will be generally as described previously, with one or more apertures therethrough so that the conductive layers on the upper and lower members can come into contact when the mat is compressed.
Finally, there is provided hereinafter a method of manufacturing hermetically sealed binary switches which utilizes bi-directional heating accompanied by a concomitant bi-directional vacuum effect to create raised areas in the upper and, preferably also the, lower surface of a mat. In more particular, according to the preferred embodiment a mat that consists of alternating polyester and polyethylene members is placed in a heated press, wherein heat is preferably applied bi-directionally (e.g., from above and below). While the press is closed and the mat is being compressed and heated, a vacuum force is applied which tends to pull apart the heat-softened outer members of the mat, and draws those members into a pattern of one or more depressions that have been formed in a special platen mold. These depressions or recessed region(s) are designed to become embossments or protrusions in the finished product. The preferred final step is to rapidly cool the recently-formed mat to room temperature, thereby permanently setting the imprint of the platen into the surface of the mat.
Of critical importance for purposes of one preferred manufacturing embodiment is that the mat be formed by placing the various layers together into a packet and heat-sealing the unit along its periphery, preferably using heat that is simultaneously applied from both sides (i.e., from the directions of both the upper and lower member). It is a further preferred aspect that vacuum be used to pull apart the upper and lower laminar members of the mat during heat sealing, thereby creating pockets(s) or protuberance(s) in the outer surfaces of the mat and rarifying the air remaining therein.
The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Further, the disclosure that follows is intended to be pertinent to all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.
While the instant invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.